Solar energy system and solar collector therefor

ABSTRACT

A solar collector for a solar energy system comprises a solar absorber for converting solar radiation into heat, a heat transfer fluid for transferring heat from the solar absorber, at least one passage for flow of the fluid in contact with the solar absorber surface, and apparatus for creating a relative vacuum in the at least one passage so as to minimize the creation of a stagnant boundary layer of the fluid when it is pumped through the at least one passage. The at least one passage is preferably formed by a convoluted surface on the solar absorber which defines at least one groove, and a flexible sheet which overlies the convoluted surface and sealingly engages the surface through the action of a vacuum. The heat transfer fluid preferably is selected from the group of mineral oil, aliphatic hydrocarbon oils, and silicone oils.

FIELD OF THE INVENTION

The present invention relates in general to solar energy systems, and inparticular to systems comprising solar heat collectors mounted on solartrackers and heat engines adapted to operate with heat energy suppliedby solar collectors.

BACKGROUND OF THE INVENTION

Although fossil fuels are currently the world's major source of energy,the increasing cost of fossil fuels and the increasing uncertaintyregarding the availability of oil, the most readily used form of fossilfuels, have generated an ever increasing demand for alternative forms ofenergy. Concern over the environmental impact of coal and nuclearenergy, as well as concern over the safety of nuclear energy has led toa growing interest in solar energy.

The approaches to harnessing solar energy have been many and varied. Ofmost pertinence to the present invention are thermal approachesutilizing solar heat collectors and thermodynamic motors or heatengines.

Typically, conventional solar heat collectors basically comprise a heattransfer fluid, commonly water, and some form of solar absorberapparatus for converting solar radiation to heat radiation, although insome solar heat collectors the heat transfer fluid also functions toconvert the solar radiation to heat radiation. Examples of the formertype of collector are disclosed in U.S. Pat. Nos. 3,215,134 (Thomason);3,965,887 (Gramer et al.); 4,030,478 (Beaver, Jr.); 4,038,967 (Stout etal.); 4,067,316 (Brin et al.); 4,086,912 (Freeman); and 4,106,482(Savage et al.). Examples of the latter type of collector are disclosedin U.S. Pat. Nos. 4,062,351 (Hastwell); 4,134,389 (McClintock); and4,158,355 (Spitzer). Of the collectors which segregate the heatcollecting and heat transfer functions several shield the heat transfermedium from exposure to the sun. The collectors disclosed in the Grameret al., Stout et al., Brin et al., and Savage et al patents are of thistype. The efficiency of such collectors is limited because there isnothing to usefully absorb the heat which is radiated from the collectorback toward the sun and away from the heat transfer medium.

Several specific features have been incorporated into conventional solarheat collectors in order to improve the efficiency thereof. Asexemplified by the Thomason collector, the heat collector surface hasbeen configured in an irregular, nonplanar shape to provide forchannelization of the heat transfer liquid so as to minimize thevolume-to-surface ratio thereof. An irregular configuration has alsobeen employed wherein a plurality of angularly disposed planar surfacesare provided which allow the solar angles of incidence either to bedecreased or to be increased to cause any reflection of solar radiationfrom the collector surface which occurs to be back onto the collectorsurface rather than back to the atmosphere. However, the efficiency ofsuch collectors is reduced because a uniform fluid flow over the entireheat absorbing surface has heretofore not been obtained.

A further feature of conventional solar collectors is the provision of arelatively transparent sheet, which may be in the form of a flexiblemembrane, overlying or covering the absorber surface. One commonfunction of such a sheet is to reduce uncontrolled reradiation andconvection currents. Another common function is to decrease theundesired effects of vaporization of the heat transfer fluid. However,conventional collectors having such covering sheets lose efficiencythrough absorption of solar energy in those sheets which are thickenough to withstand the pressures created within the collectors when theheat transfer fluid is pumped therethrough at an accelerated rate, orthrough the inability of those sheets which are flexible to contain theheat transfer fluid properly when a flow rate greater than a trickle isdesired or when those collectors utilizing a minimal flow rate aretilted at steep angles. Another disadvantage heretofore of usingcovering sheets with collectors having channelized fluid flow has beenthe necessity of mechanically sealing the covering sheets to irregularlyconfigured collector surfaces in order to adequately contain and controlthe flow.

Another approach to improving the efficiency of conventional solarcollectors is disclosed in the Gramer et al patent. Thermal transfer isimproved between the solar absorber and the heat transfer liquid byproviding rectangular fluid passages having specified dimensions, and byaccelerating the heat transfer fluid flow through the passages tomaintain a laminar flow of substantially constant cross-sectional area,so as to minimize eddy currents.

Yet another approach to improving the efficiency of conventional solarcollectors has been to provide tracking apparatus for maintaining thecollector in a predetermined orientation with respect to the sun duringthe transit thereof through the sky. Examples of such trackers aredisclosed in U.S. Pat. Nos. 1,938,003 (Arthuys et al.); 4,044,752(Barak); and 4,147,154 (Lewandowski).

However, despite these and other features, conventional solar heatcollectors have not achieved sufficiently high operating efficiencies tojustify the costs of manufacture, installation, and operation forwidespread use.

With regard to conventional heat engines, such devices have employedeither a single volatile fluid or a volatile fluid which is mechanicallycoupled to a dense fluid. Examples of single-fluid heat engines aredisclosed in U.S. Pat. Nos. 243,909 (Iske et al.); and 3,983,704(McFarland); and in an article entitled "Wally Minto's Wonder Wheel,"appearing in the March 1976 issue of Popular Science at page 79.Examples of two-fluid heat engines are disclosed in U.S. Pat. Nos.3,984,985 (Lapeyre); and 4,074,534 (Morgan). However, both types of heatengines have exceedingly low operating efficiencies and have neverproved commercially feasible.

SUMMARY OF THE INVENTION

These and other disadvantages of the prior art are overcome by a solarenergy system constructed in accordance with the present invention,which comprises an improved solar heat collector and heat engine whichare low in cost, easy to manufacture, and which provide superioroperating efficiencies; and an improved solar tracker of exceedinglysimple construction and effectiveness.

In accordance with one aspect of the present invention, the solar heatcollector is provided with a heat transfer fluid, such as mineral oil,an aliphatic hydrocarbon oil or a silicone oil, which is substantiallytransparent to shortwave infrared (IR) solar radiation and has a lowreradiation factor for long-wave IR heat, and which is disposed inoverlying contact with the radiation receiving surface of a solarabsorber.

In accordance with another aspect of the present invention, the solarheat collector is configured so as to define at least one passage forflow of heat transfer fluid in contact with a solar absorber and isprovided with apparatus for creating a relative vacuum in the at leastone channel so as to minimize the creation of a stagnant boundary layerof the heat transfer fluid in contact with the solar absorber when theheat transfer fluid is pumped through the at least one passage.

In accordance with still another aspect of the present invention, thesolar absorber has a convoluted surface defining at least one groove,and a sheet, which is preferably flexible, sealingly engages theconvoluted surface through the action of a vacuum such that the sheetand the at least one groove form a corresponding at least one passagefor the flow of heat transfer fluid therethrough. Advantageously, theconvoluted surface is the radiation receiving surface of the absorber,and the sheet is substantially transparent to solar IR radiation.

In accordance with a further aspect of the invention, solar trackingapparatus constructed in accordance with the present invention comprisesat least one chamber containing a volatile fluid, shading forcontrolling the degree to which each chamber is exposed to the sun independence on the position of the sun so as to control the extent towhich the fluid is vaporized due to solar heating, and couplingapparatus for coupling the expansive force generated by vaporization ofthe fluid to a workpiece to control the position, orientation, and/oroperation thereof.

Preferably, solar apparatus constructed in accordance with the presentinvention comprises a base pivotably mounted with respect to a pivotaxis, first and second chambers mounted to the base in counter-balancingrelationship with respect to the pivot axis, a conduit connected betweenthe chambers for transfer of fluid therebetween, a volatile fluiddisposed in the chambers, and shading for controlling the degree towhich each chamber is exposed to the sun such that a differential vaporpressure is created between the chambers in dependence on the positionof the sun which causes a predetermined transfer of fluid between thechambers. The transfer of fluid in turn causes the base to pivot into apredetermined orientation with respect to the position of the sun.

Advantageously, mounting apparatus is provided which produces acounterbalancing biasing force when the base is pivoted at an inclinedangle with respect to a predetermined position.

In accordance with a still further aspect of the present invention, aheat engine constructed in accordance with the present inventioncomprises first and second tanks radially mounted for rotation withrespect to an axis of rotation and so as to be spaced from each other, aconduit connecting the tanks together for transfer of fluidtherebetween, a heated, relatively heavy fluid disposed in the tanks fortransfer therebetween, and apparatus for introducing a relativelyvolatile fluid in a condensed state into direct vaporizing contact withthe heavy fluid at predetermined times during the rotation of the tankssuch that expansion of the vaporized volatile fluid causes heavy fluidto be cyclically transferred between the tanks so as to maintainrotation thereof.

Advantageously, the tanks are diammetrically opposed to each other, andthe volatile fluid introducing apparatus comprises apparatus forcondensing first and second portions of the volatile fluid, and aconduit connecting each condensing apparatus to the corresponding tankfor transfer of the volatile fluid portions to the respective tanks whenthe tanks are at least substantially at the lowermost positions thereof.

A solar energy system constructed in accordance with the presentinvention provides superior operating efficiencies far exceeding thoseof conventional systems with apparatus which is exceptionally simple andinexpensive to manufacture, easy to operate, and extremely reliable.

In particular, the performance of the solar collector of the presentinvention far exceeds that of conventional flat collector panels. Anexperimental prototype mounted in a fixed orientation at a Los Angeles,Calif. site has been producing a thermal output which is almost twicethat predicted for optimal solar panel performance in the Los Angelesarea by the Dow-Corning Corporation in its The Solar Decision Book,published in 1978, and which is over twice the average output of thecollectors tested by the Southern California Gas Company in 1979.

The solar tracker of the present invention also offers superiorperformance. Operating with the sun itself as its only source of power,and without the need for exotic heat or light sensitive materials, as isthe case with conventional solar-powered trackers, an experimentalprototype of applicant's solar tracker has improved the performance ofthe aforementioned prototype of applicant's solar collector over 225% ascompared with the output obtainable when the collector is maintained ina fixed orientation.

Similarly, the heat engine of the present invention is capable ofoperating efficiencies at least equal to those of commercial powergenerating steam turbines, and is particularly adapted to operate withheat energy obtained from the sun.

Other features and advantages of the invention will be set forth in, orapparent from, the detailed description of preferred embodiments foundhereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, like elements have been designated with like referencenumerals. In addition, for the sake of clarity, various features havebeen omitted and/or only certain features have been shown in phantom inparticular views.

FIG. 1 is a schematic block diagram of a solar energy system constructedin accordance with the present invention.

FIG. 2 is a schematic block diagram of a solar collector constructed inaccordance with the present invention.

FIG. 3 is a top plan view, partially broken away, of a portion of thesolar collector illustrated in FIG. 2.

FIG. 4 is a cross-sectional view taken generally along the line 4--4 andpartially broken away of the solar collector apparatus shown in FIG. 3.

FIG. 5 is an enlarged detail view of a portion of FIG. 4.

FIG. 6 is a cross-sectional view, taken generally along line 6--6 andpartially broken away, of the solar collector of FIG. 3.

FIG. 7 is a schematic block diagram of a solar tracker constructed inaccordance with the present invention.

FIG. 8 is a diagrammatic top perspective view of a first embodiment of asolar tracker constructed in accordance with the present invention foruse with the solar collector illustrated in FIGS. 2-6.

FIGS. 9-11 are bottom perspective views of a portion of the solartracker shown in FIG. 7 showing three different orientations thereof.

FIG. 12 is a diagrammatic bottom perspective view of a second embodimentof a solar tracker constructed in accordance with the present invention.

FIG. 13 is a diagrammatic side elevation view of a third embodiment of asolar tracker constructed in accordance with the present invention.

FIG. 14 is a diagrammatic top perspective view of a portion of a furtherembodiment of a solar tracker constructed in accordance with the presentinvention.

FIG. 15 is a top plan view of a portion of the solar tracker illustratedin FIG. 8.

FIG. 16 is a top perspective view of still another embodiment of a solartracker constructed in accordance with the present invention.

FIG. 17 is a diagrammatic side elevation view of a heat engineconstructed in accordance with the present invention.

FIG. 18 is a diagrammatic end elevation view, selectively cut away, of amodified two tank embodiment of the heat engine shown in FIG. 17 whichincludes a combined heating and cooling system adapted for use with heatenergy supplied by a solar collector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a solar energy system constructed in accordancewith the present invention generally comprises a solar collector 20 forobtaining heat from solar radiation; a solar tracker 40 for controllingthe position, orientation and/or operation of an object, apparatus orthe like in dependence on the position of the sun, preferred embodimentsof which are particularly adapted to control the orientation ofcollector 20; and a heat engine 80 for converting heat energy tomechanical or other forms of energy, preferred embodiments of which areparticularly adapted to operate with heat energy supplied from collector20.

Referring to FIGS. 2-6, solar collector 20 generally comprises a frame22, a solar absorber 24 mounted on frame 22, at least one relativelytransparent sheet 26 mounted on frame 22 so as to cover or overlie thesurface 30 of absorber 24 which faces the sun, a heat transfer fluid 28for transferring heat from absorber 24, and a flow control module,generally denoted 27 and connected to frame 22 and a thermal load (notshown) by conduits 29, for creating a vacuum and pumping fluid 28between absorber 24 and sheet 26.

As shown, frame 22 advantageously is rectangular in shape to maximizethe collector surface area, and is made of material such as a plastic orpolyester fiberglass to minimize the weight, manufacturing cost andthermal expansion 23, such as plastic foam, disposed beneath absorber 24to minimize undesired heat transfer from absorber 24 to other than heattransfer fluid 28.

Absorber 24 is made of any conventional material so as to function as a"black body" and convert the short wave infrared (IR) and,advantageously, other components of solar radiation into heat of longwavelength. Although absorber 24 can be made of a metallic, thermallyconductive material with a selective coating, as is conventional, tomaximize the thermal efficiency thereof, absorber 24 advantageouslycomprises a thermally nonconductive material, such as vinylesterimpregnated with carbon black, which is applied as a coating (not shown)to a substrate made from fiberglass or the like to provide aninexpensive, light-weight, and stable absorber.

As shown, surface 30 of absorber 24 has a convoluted configurationforming a plurality of alternating ridges or teeth 31 and grooves 32. Asshown, grooves 32 preferably are identically configured, parallel and ofequal lengths to ensure uniformity of fluid flow therethrough. Surface30 is also formed with transversely extending cylindrical depressions ortroughs 34 at each end of grooves 32 which function as distributionmanifolds to connect grooves 32 with pump conduits 29 such that heattransfer fluid 28 can be pumped through grooves 32 in either direction.Advantageously, conduits 29 are connected to the corresponding trough 34at opposite ends thereof, as shown, in order to ensure that the flow offluid 28 is uniform from groove to groove.

Teeth 31 and grooves 32 preferably are configured so as to provide anoptimum solar acceptance angle, and to maximize the surface-to-volumeratio of grooves 32 without sacrificing the flow rate capabilitythereof. As will be appreciated by those of ordinary skill in the art,the provision of a convoluted surface 30 provides a surface with agreater effective collecting area than a planar surface, which resultsin collector 20 operating at a lower temperature, and thus with greaterefficiency. Further, a convoluted surface 30 increases the thermaltransfer efficiency of collector 20 by increasing the percentage offluid 28 which is in surface contact with absorber 24. A furtheradvantage of maximizing the surface-to-volume ratio of grooves 32 isthat the amount of fluid 28 passing through collector 20 at any one timeis minimized, thereby reducing the operating weight of collector 20.This advantage is of particular importance in "retrofit" situations.

Preferably, teeth 31 have thin projecting or vertex edges to provide"knife edge" contact with sheet 26 and thus minimize thermal lossesresulting from heat transferred to sheet 26 rather than fluid 28.Triangular or saw-tooth shaped teeth 31 and grooves 32 having vertexangles of 60° have proven to be advantageous. Flatter vertex angles arenot preferred because (1) the decreased solar acceptance angle makes theorientation of collector 20 with respect to the sun more critical; (2)the flow rate tends to decrease and the flow rates from groove to groovetend to be uneven; (3) the potential for groove blockage by foreignmatter is increased; and (4) the structural reinforcement provided bythe saw-tooth configuration is diminished. Steeper vertex angles areadvantageous in that they provide improved acceptance angles, but theydo present greater manufacturing difficulties. Further, vertex angleswhich are too steep present the same problems noted hereinabove thatoverly flat vertex angles present.

In an experimental prototype of absorber 24 approximately 8.5 feet (2.6meters) long and four feet (1.2 meters) wide, a surface 30 having ninegrooves 32 per inch (3.54 grooves per centimeter) which are 0.090 inches(0.23 cm) deep and 8 feet (2.4 meters) long has proven to be mostsatisfactory. Further, an embodiment of troughs 34 which is 1.75 inches(4.44 cm) in diameter has proven advantageous with the experimentalprototype of absorber 24 described hereinabove.

Sheet 26 preferably is transparent to shortwave IR radiation, reflectiveand nonabsorptive to long wave heat losses, heat resistant, stable withrespect to ultraviolet (UV) radiation for long life, tear resistant,substantially impermeable, and has a relatively high tensile strengthand a low creep coefficient to minimize undesired deformation. Althoughsheet 26 can be substantially stiff or rigid, additional advantages areobtained when sheet 26 is in the form of a flexible membrane. Anembodiment of sheet 26 made of 2 mil (0.05 mm) thick "Tedlar" or"Teflon" fluorocarbon material has proven to be particularlyadvantageous. "Tedlar" is generally preferred because of its lower cost,but "Teflon" is preferred when collector 20 is operated at temperaturesabove approximately 250° F. (121° C.).

Frame 22 preferably is gas-tight and sheet 26 is sealingly mounted toframe 22 in overlying relationship with respect to absorber surface 30such that a relative vacuum may be created between sheet 26 and absorber24 which causes sheet 26 to engage the vertex edge of each absorbertooth 32 in liquid-tight sealing contact such that sheet 26 and absorbergrooves 32 form a plurality of discrete channels or passages 35 forfluid flow. To minimize the effects of differential thermal expansionand contraction, sheet 26 preferably is joined to a plastic orfiberglass embodiment of frame 22 using high temperature acrylic tape orthe like and a covering of fiberglass (not shown).

Passages 35 preferably have uniform configurations such that fluid flowthrough all of the passages is uniform and does not vary from passage topassage. Hence sheet 26 advantageously has sufficient stiffness tominimize sagging, or other deformation or distortion of the sheetportion overlying absorber grooves 32 which would impede, or otherwiseaffect the uniformity of flow through passages 35. However, sheet 26preferably also has sufficient flexibility to facilitate sealingengagement of sheet 26 with absorber teeth 31 when sheet 26 is subjectedto a vacuum, and sufficient elasticity to accommodate dimensionalchanges in the collector caused by diurnal temperature changes.

When a membrane embodiment of sheet 26 is employed, sheet 26advantageously is secured to frame 22 under sufficient tension tominimize surface irregularities therein which would impede or otherwiseinterfere with uniform fluid flow through passages 35. In addition,collector 20 preferably is further provided with thin, rigid plates 36which overlie or cover troughs 34 such that the bottom surfaces ofplates 36 are substantially coplanar with the vertex edges of teeth 32.Plates 36 support sheet 26 where it spans troughs 34 to minimize anysagging of sheet 26 in the presence of a vacuum which would restrict anyof the interfaces between grooves 32 and troughs 34 and thus interferewith uniform fluid flow through all of the passages 35. Plates 36preferably also are coated in a conventional manner so as to function asheat absorbers. Consequently, troughs 34 and the fluid 28 disposedtherein can actively participate in the heat collection process.

As will be appreciated by those of ordinary skill in the art, theutilization of a vacuum in combination with a convoluted collectorsurface and a flexible covering sheet in the manner describedhereinabove allows heat transfer fluid 28 to be pumped across absorbersurface 30 in a channelized flow which is uniform over the entiresurface and which is at a uniform and accelerated flow rate without theneed, in order to control flow, for rigid, thick, energy-absorbingcovering sheets, or the need for specialized mechanical sealingarrangements between the covering sheet and the portions of the absorbersurface separating the passages. Further, the vacuum creates a pressuredifferential between the outer or atmospheric-facing side, and the inneror absorber-facing side of sheet 26 which allows fluid 28 to be pumpedthrough passages 35 at an elevated fluid pressure with minimumdistortion of sheet 26. Since fluid 28 flows through passages 35 underfluid pressure, fluid 28 is "squeezed" into intimate contact with theentire surface of each groove 32 so as to improve heat transfer fromabsorber 24 to fluid 28. Still further, the flow rates through passages35 are maintained uniform for all orientations of collector 20 withoutthe need for special manifold orifices or adjustments in flow rates toaccommodate changing tilt angles.

Although collector 20 is operable with a single sheet 26, collector 20advantageously is provided with at least one additional sheet, andpreferably two additional sheets 37, as shown, sealingly mounted onframe 22 overlying sheet 26 and in spaced relationship thereto. Sheets37 function to provide insulation and to minimize heat convection andradiation by creating regions 38 of dead air between sheet 26 and theenvironment. Sheets 37 thus preferably have the same characteristicsnoted above as sheet 26. However, since sheets 37 are not subject to avacuum, flexibility is not particularly advantageous. Moreover, sincethe outermost sheet 37 is subject to winds and the like, it is desirablethat at least the outermost one of sheets 37 be substantially rigid andinflexible. It is to be noted, though, that the same type of flexiblemembrane noted hereinabove as being suitable for sheet 26 can alsoadvantageously be used for both sheets 37, provided that sheets 37 aresecured to frame 22 under sufficient tension to render sheets 37effectively rigid and inflexible. It is to be further noted in thisregard that the use of "Tedlar" sheeting is especially preferred forsheets 37 because it has been found that "Tedlar" exhibits a heatshrinking tendency which causes sheets 37 made from "Tedlar" to becomequite taut over a period of time as collector 20 is operated at normalelevated operating temperatures.

Preferably, the spacing between sheets 37 and between the inner sheet 37and sheet 26 is minimized to limit convection air currents withinregions 38. However, sufficient spacing preferably is provided toprevent contact between any of the sheets 26 and 37 due to gravity, windand the like. When a membrane embodiment of sheets 37 made from "Tedlar"is employed, a spacing of one-half inch (1.27 cm) has provenadvantageous in practice.

Heat transfer fluid 28 may be any fluid which is effectively transparentto solar IR radiation at a film thickness corresponding to the depth ofchannels 35, and which is a poor radiator, i.e., has a low reradiationfactor, for long wave IR heat energy. In the experimental prototype ofcollector 20 described hereinabove, water has proven quite satisfactoryas fluid 28, but various oils, such as mineral oil, aliphatichydrocarbon oils, and particularly silicone oils are preferred sincethey provide substantially improved performance. The use of oils has theadditional advantages of preventing permeation and clouding of sheet 26and permitting operation of collector 20 at both higher and lowertemperatures as desired.

Flow control module 27 advantageously comprises a conventionalcirculating pump 27A connected to a reservoir 27B of heat transfer fluid28 and to conduits 29, a conventional vacuum source 27C connected toconduits 29, and conventional vacuum-responsive pressure switches,generally denoted 27D, connected so as to monitor the pressure inconduits 29 and so as to control the operation of pump 27A and source27C. Conduits 29, frame 22, and pump 27A and reservoir 27B of controlmodule 27 are connected so as to form a gas-tight closed loop from whichair may be evacuated. Switches 27D are configured such that vacuumsource 27C operates at any time the sensed relative pressure within theclosed loop exceeds a predetermined maximum level corresponding to adesired level of relative vacuum, and such that circulating pump 27Aoperates only when the sensed relative pressure within the closed loopis below the aforesaid predetermined maximum value. Consequently, whenflow control module 27 is initially actuated, vacuum source 27Cinitially operates to evacuate the system. Once the predetermined degreeof relative vacuum has been attained, and sheet 26 has thus sealinglyengaged absorber surface 30 to form passages 35, circulating pump 27A isactuated to begin circulating heat transfer fluid 28 through the system.Pump 27A thereafter operates continuously while collector 20 iscollecting heat. Once pump 27A has commenced pumping, vacuum source 27Ccontinues to operate until all of the air has been flushed from passages35 and conduits 29 and they have become completely filled with fluid 28.Source 27C thereafter operates only when the relative pressure withinthe closed loop increases beyond the predetermined level due to theincreased temperatures within the closed loop which are caused byoperation of the collector, or when a leak develops. As will beappreciated by those of ordinary skill in the art, flow control module27 advantageously also is provided with conventional thermallyresponsive control apparatus to control pump 27A in dependence on thetemperature of fluid 28.

The pumping capacity of circulating pump 27A preferably is sufficient tocreate the desired flow rate through channels 35. Advantageously, theflow rate is maximized to obtain the minimum temperature differentialacross collector 20 consistent with the achievement of the highestoverall energy efficiency of the system. In other words, the flow rateshould not exceed the rate at which the marginal utility of an increasedrate is not warranted because the power usage of the pump which would benecessary to obtain the increased flow rate would be disproportionate tothe additional heat output which would be obtained as a result of theincreased flow rate. In addition, as will be appreciated by those ofordinary skill in the art, a further practical limitation on achieving apreferred flow rate is the cost of the necessary pumps. However, it isto be noted that the provision of a convoluted absorber surface 30 andsealed channels 35 for fluid flow reduces the flow rates which arerequired to achieve satisfactory collector performance.

Advantageously, the pumping capacity of vacuum source 27C is sufficientto create a vacuum which minimizes the "boundary layer" effect whichtends to occur when heat transfer fluid 28 is pumped through passages35. As will be appreciated by those of ordinary skill in the art, theboundary layer effect causes some portion of fluid 28 in channels 35 tobecome stagnant and to remain in intimate contact with collector surface30, such that the main body of fluid 28 flows over the boundary layerand absorbs heat therefrom rather than from the collector surface.Further, for use of collector 20 with tracker 40 to be describedhereinbelow, the vacuum should be sufficient to allow tilting ofcollector 20 without affecting the flow rate.

As will be appreciated by those of ordinary skill in the art, the use ofa vacuum has the further advantages of allowing operation of collector20 at a location both above and below the location of pump 27A,minimizes the leakage of fluid 28 and facilitates detection of leaks,and allows sheet 26 to be made of a thin, flexible material which ishighly transparent to shortwave IR radiation, light weight, and bothsufficiently elastic to accommodate dimensional changes in the collectorcaused by diurnal temperature changes and sufficiently rigid whensealingly engaged with surface 30 of absorber 24 to allow heat transferfluid 28 to be pumped through passages 35 at the desired flow ratewithout distortion of passages 35.

In the experimental prototype of collector 20 described hereinabove, avacuum of eight inches (20.32 cm) of mercury, and a flow rate of two tothree gallons per minute (7.6-11.4 liters per minute) through channels35 has proven most satisfactory. The measured back pressure of theaforesaid experimental prototype of collector 20 is 7.3 feet (2.22meters), and the aforementioned vacuum and flow rate parameters wereobtained with an embodiment of pump 27A capable of pumping 320 gallonsper hour (1211 liters per hour).

In addition, for use of collector 20 with tracker 40 describedhereinbelow, collector 20 further comprises a conventionalgravity-directed flow direction control circuit 39 mechanically linkedto frame 22 and connected between pump 27 and pump conduits 29 tocontrol the flow of fluid 28 through channels 35 such that fluid 28always flows toward the upper end of surface 30.

Referring to FIG. 7, solar tracker 40 basically comprises at least onechamber 42 containing a volatile fluid 44, a shading arrangement,generally denoted 46, for controlling the degree to which the at leastone chamber 42 is exposed to the sun in dependence on the position ofthe sun, and thereby controlling the extent to which fluid 44 isvaporized due to solar heating of the at least one chamber 42, andapparatus, generally denoted 48, for coupling the expansive forcegenerated by vaporization of fluid 44 in the at least one chamber 42 toan object, apparatus or the like, generally denoted 49, to control theposition, orientation, and/or operation thereof.

Referring to FIGS. 8-16, practical embodiments of solar tracker 40 willnow be described which are adapted for use with collector 20 describedhereinabove to maintain collector 20 at an optimum orientation withrespect to the sun throughout the day for maximum solar energycollection.

The practical embodiments of tracker 40 generally comprise a base 50 forsupporting collector 20, mounting apparatus, generally denoted 52, forpivotably mounting base 50 with respect to at least one pivot axis, apair of tanks 54 for each pivot axis mounted to base 50, a conduit 56for each pair of tanks 54 connecting the tanks together for the transferof fluid therebetween, a shading arrangement, generally denoted 58, foreach tank 54 for controlling the degree to which the associated tank 54is exposed to the sun in dependence on the position of the sun, and avolatile fluid 71 disposed in each pair of tanks 54 for transfertherebetween.

Any conventional type of supporting apparatus which allows tanks 54 tobe symmetrically mounted with respect to the at least one pivot axis ina counterbalancing relationship advantageously comprises base 50. Whenthe preferred embodiments of collector 20 described hereinabove aremounted on solar tracker 40, collector frame 22 advantageouslyconstitutes base 50.

Any conventional type of mounting apparatus can constitute mountingapparatus 52. Preferably, mounting apparatus 52 is configured such thata counteracting biasing force is produced when base 50 is pivoted so asto be inclined with respect to a predetermined equilibrium or stableposition thereof, which biasing force acts to urge base 50 to return tothe stable position. The biasing force advantageously is such that themagnitude thereof is proportional to the degree to which base 50 ispivoted from the stable position thereof.

A first preferred embodiment of mounted apparatus 52 is illustrated inFIGS. 8-11 which allows pivoting of base 50 with respect to a singlepivot axis, and thus which is adapted for use with embodiments oftracker 40 utilizing a single pair of tanks 54. The first illustratedembodiment of apparatus 52 comprises a vertically oriented pedestal 51mounted to the ground or other such support, a cross-bar or otherplatform 53 for supporting base 50 mounted to the distal end of pedestal51, first and second toothed wheels 55 fixedly mounted by means ofbrackets 59 to base 50 in spaced relationship to each other and so as todefine a north-south extending pivot axis 60, and first and secondtoothed tracks 57 which project from platform 53 in spaced relationshipto each other so as to engage the corresponding wheels 55. Wheels 55preferably are aligned with the center of gravity, or balance point, ofbase 50, as determined when base 50 is operatively loaded. Further, inorder to provide the aforementioned biasing force, wheels 55 are mountedto base 50 such that pivot axis 60 is disposed relatively higher thanthe balance point of base 50. The vertical spacing between pivot axis 60and the balance point of base 50 preferably is such that the equilibriumorientation of base 50 is a relatively horizontal orientation. A spacingof one-half inch (1.27 cm) has proved advantageous with the experimentalprototype of collector 20 described hereinabove mounted on an embodimentof tracker 40 utilizing the tube embodiment of tanks 54 describedhereinbelow.

As shown in FIGS. 9-11, respectively, rotation of wheels 55 causespivoting of base 50 with respect to axis 60 between an eastwardly-facinginclined position and a westwardly-facing inclined position. Rotation ofwheels 55 further causes displacement thereof along tracks 57 such thatplatform 53 does not interfere with pivoting of base 50.

A second preferred embodiment of mounting apparatus 52 is illustrated inFIGS. 12 and 13 which allows pivoting of base 50 with respect to anypivot axis, and thus which is particularly adapted for use withembodiments of tracker 40 utilizing at least two pairs of tanks 54. Thesecond illustrated embodiment of apparatus 52 simply comprises avertically oriented coil compression spring 61, one end of which ismounted on pedestal 51 so as to be spaced from the ground or other suchsupport, and the other end of which is mounted to base 50 coaxially withthe balance point thereof. As will be appreciated by those of ordinaryskill in the art, bending or flexing of spring 61 with respect to thelongitudinal axis thereof produces the aforementioned biasing forcewhich acts to urge tracker base 50 back from a relatively inclinedposition to the stable, relatively horizontal position thereof.

As shown in FIG. 13, base 50 advantageously is configured to support twocollectors 20 which are symmetrically disposed on opposite (north andsouth) sides of an east-west extending pivot axis, and such that base 50pivots about a point 70 which is spaced above the balance point of base50 as determined when collectors 20 are loaded on base 50. As will beappreciated by those of ordinary skill in the art, the aforementionedbiasing force is provided both by the action of spring 61 and thedisposition of the pivot axis above the combined balance point.

A third preferred embodiment (not shown) of mounting apparatus 52comprises conventional gimbals on which base 50 is suspended.

Each pair of tanks 54 is mounted to base 50 such that tanks 54 aresymmetrically disposed on opposite sides of an imaginary plane definedby the associated pivot axis so as to be in counterbalancingrelationship therewith. In the two tank embodiment of tracker 40illustrated in FIG. 8, tanks 54 are mounted along an east-west axis oforientation for diurnal tracking of the sun. In the four tank embodimentof tracker 40 illustrated in FIGS. 13 and 16, one pair of tanks 54 ismounted along an east-west axis of orientation for diurnal tracking ofthe sun and the other pair of tanks 54 is mounted along a north-southaxis of orientation for seasonal tracking of the sun. The degree towhich tracker base 50 will tilt, with respect to a given pivot axis, isdetermined by the angle of inclination at which the differential torqueapplied thereto as a result of a transfer of fluid 71 between thecorresponding tanks 54 is counterbalanced by the aforementioned biasingforce which is produced. In order to accommodate the relatively greaterdegree of change in the diurnal position of the sun as compared to theseasonal position of the sun, the pair of tanks 54 having an east-westaxis of orientation has a relatively greater amount of fluid 71 disposedtherein and/or has a relatively greater spacing between the tanks 54,than does the pair of tanks 54 having a north-south axis of orientation.In both the two tank and the four tank embodiments of tracker 40, eachpair of tanks 54 is disposed so as to be aligned with a point of supportprovided by mounting apparatus 52. Thus, in the two tank embodiment ofFIG. 8, tanks 54 are aligned with toothed tracks 55 of mounting platform53, and in the four tank embodiment of FIGS. 13 and 16, tanks 54 arealigned with the balance point of base 50.

Tanks 54 may have any desired conventional configuration. Tanks 54advantageously are configured in the form of relatively narrow diameter,elongate tubes which project vertically upward from tracker base 50, asshown in FIGS. 8, 13, 14, and 15, so as to maximize the torquedifferential which is produced by the shift of a given mass of fluid 71between associated tanks 54. Tubular versions of tanks 54 four inches(10.2 cm) in diameter and four feet (1.2 m) in length have provensatisfactory with the practical embodiment of collector 20 describedhereinabove. Alternatively, tanks 54 advantageously are configured inthe form of relatively squat pods or the like which extend parallel tobase 50, as shown in FIG. 16, so as to minimize the vertical profile,and hence the space requirements, of tracker 40.

As shown in FIGS. 8 and 13, conduit 56 preferably is connected to theassociated tanks 54, for example, at the bottoms thereof, so as toensure that only fluid 71 in the liquid state thereof is transferred byconduit 56. Alternatively, conduit 56 communicates with fluid 71 in atank 54 via a weighted inlet tube (not shown) which is mounted withinthe tank such that the distal end of the tube is displaced by the actionof gravity to the lowermost point of the tank interior regardless of thetank's orientation. A further conduit 62 controlled by a valve 63advantageously also is provided for each pair of tanks 54, as shown inFIG. 7, connecting the upper portions of associated tanks 54 so as toallow the gas pressure, and thus the levels of fluid 71, in tanks 54 tobe initially equalized. After tanks 54 have been equalized, valve 63 isclosed during operation of tracker 40 to prevent fluid transfer betweenthe associated tanks 54 through conduit 62.

Each shading arrangement 58 is configured such that selected ones oftanks 54 are heated by the sun's radiation at different times during theday and a temperature imbalance is created between connected tanks whichresults in a transfer of fluid 71 therebetween, and hence a shift in theweight distribution of fluid 71 with respect to the corresponding pivotaxis.

In order to maintain base 50 of the two tank embodiment of tracker 40substantially orthogonal to, or in "high noon" relationship to the sun'sradiation, tanks 54 are shaded by the corresponding shading arrangement58 such that solar exposure of the east tank from the east andsoutheast, and solar exposure of the west tank from the west andsouthwest, are ineffective to heat the respective tanks. In order tomaintain the four tank embodiment of tracker 40 properly aligned withrespect to the sun, the corresponding shading arrangements 58advantageously are configured to shade the east and west tanks 54 fromeastern and western exposure, respectively, and the north and southtanks 54 from northern and southern exposure, respectively.

Each shading arrangement 58 advantageously comprises either a treatedportion of the outer surface of the corresponding tank 54 which definesa relatively reflective region 64 thereon, as shown in FIG. 14, or aseparate panel or screen 66 mounted adjacent the corresponding tank 54by means of mounting brackets 67, as shown in FIGS. 8, 13, 15, and 16.

As shown in FIGS. 8, 13, and 15, each screen 66 advantageously has aplanar configuration and is mounted parallel to the longitudinal axis ofthe corresponding tank 54, and diagonally with respect to thecorresponding axis of orientation. As shown in FIG. 16, each screen 66preferably is also provided with a cap 69 or the like to shade the topor upwardly facing surface of the corresponding tanks 54 for use withembodiments of tank 54 having a substantial horizontally disposed top orupper surface in addition to vertically disposed surfaces, which uppersurface would cause undesired heating of fluid 71 if it were exposed tothe sun's radiation.

As will be apparent to those of ordinary skill in the art, the durationand timing of the shading provided by a screen 66 with respect to thetransit of the sun is dependent on the angle of inclination of screen 66with respect to the corresponding tank axis of orientation and thetransverse or width dimension of screen 66. In the two tank embodimentof tracker 40, mounting screens 66 having a transverse dimension of teninches (25.4 cm) at an angle of approximately 30° with respect to theeast-west axis of orientation has proven advantageous with the tubeembodiment of tanks 54 described hereinabove.

Preferably, when a screen embodiment of shading arrangement 58 isemployed, the outer surfaces of tanks 54 are treated so as to berelatively absorptive of solar radiation, and the surface 65 of eachscreen 66 which faces the corresponding tank 54 is relativelyreflective, such that when the sun is positioned for exposure of a tank54, solar radiation is reflected from screen surface 65 onto the tank 54to enhance the radiation incident thereon, and hence the degree to whichthe tank 54 is heated.

Volatile fluid 71 preferably has a high specific gravity and a lowboiling point. Freon has proven advantageous. Preferably, tanks 54 areevacuated and a sufficient quantity of fluid 71 is introduced into eachpair of tanks 54 so as to partially fill both tanks.

As will be appreciated by those of ordinary skill in the art, shadingarrangements 58 permit selective exposure of tanks 54 to solar radiationin dependence on the position of the sun. Those tanks 54 which areexposed to the sun are heated, which causes at least some of the fluid71 disposed in the tanks to vaporize. Uneven heating of connected tanks54 creates a pressure unbalance therein which results in a displacementof unvaporized fluid 71 from the relatively hotter tank to therelatively cooler tank. The displaced fluid produces a weight imbalancewhich causes base 50 of tracker to tilt toward the sun such that theexposed surface thereof is more nearly perpendicular to the sun'sradiation.

More specifically, referring to the two tank embodiment of tracker 40illustrated in FIG. 8, the vapor pressure in tanks 54 is initiallyequalized in the manner described hereinabove by means of conduit 62 andvalve 63 such that tracker base 50 is initially balanced in a horizontalposition. As the sun rises, the east tank 54 is shaded and the west tank54 is exposed to the sun's rays. As the west tank 54 is heated, some ofthe fluid 71 is displaced from the west tank 54 to the east tank 54,which causes tracker 40 to tilt such that base 50 is in an eastwardlyfacing inclined position facing the sun. As the sun continues to riseduring the day, an increasing proportion of the east tank 54 is exposedto the sun's rays, causing a counterbalancing heating and vaporizationprocess therein which causes a shift of fluid 71 back to the west tank54, and a consequent tilting of tracker 40 back toward the horizontal asthe sun rises to the noontime position thereof, and then toward awestwardly facing inclined position as the sun begins its descent tosunset.

The aforementioned fluid shifting process continues until sunset oruntil heavy clouds reduce the heating which occurs to the point whereboth tanks 54 are cooled to substantially the same temperature. As atemperature equilibrium is reached, the partial vacuum in tanks 54causes fluid 71, substantially all of which is preferably then in aliquid state, to seek equilibrium levels in tanks 54. The resultingweight shift with respect to the corresponding pivot axis, plus thebiasing force described hereinabove which is produced when base 50 is ina non-horizontal position, cause tracker 40 to return to a leveledposition. A similar process occurs with respect to each pivot axis inthe four tank embodiment of tracker 40 illustrated in FIGS. 13 and 16.

Referring to FIGS. 17 and 18, heat engine 80 comprises at least one pairof opposed tanks 82 radially mounted for rotation about an axis ofrotation 84, a conduit 86 for each pair of tanks 82 connecting the tankstogether for transfer of fluid therebetween, a condensation chamber 88for each tank 82, a conduit 90 connecting each condensation chamber 88to the corresponding tank 82 for transfer of fluid therebetween, arelatively heavy fluid 92 disposed for transfer between connected tanks82, a relatively volatile fluid 94 disposed for transfer from eachcondensation chamber 88 to the corresponding tank 82, a heatingarrangement or system, generally denoted 96, for heating heavy fluid 92,and a cooling arrangement or system, generally denoted 98, for coolingcondensation chambers 88.

As shown, preferably at least two pairs of opposed tanks 82 areprovided, with each pair equally spaced from the adjacent pairs.Condensation chambers 88 are preferably disposed symmetrically withrespect to each other and such that each chamber 88 is diammetricallyopposed to the tank 82 to which it is connected and adjacent the tank 82opposing the tank 82 to which it is connected. As shown, conduits 86preferably are configured so as to form loop-type traps 87 which aretangentially connected to the corresponding tanks 82 such that each trap87 is disposed relatively below the associated tank 82 when the tank isdisposed in the lowermost position thereof. Conduits 86 and tanks 82preferably are also connected such that opposing tanks 82 are on theopposite sides of an imaginary plane defined by the connecting conduit86 and adjacent tanks 82 are separated by an imaginary plane defined byone of the associated conduits 86. Thus, as a pair of tanks 82 rotatesabout axis 84, each tank 82 will reach and have passed through theuppermost vertical position thereof slightly before the associatedconduit 86 reaches the vertical position thereof. The direction ofrotation of tanks 82, and hence of engine 80 when operating, is thusdetermined by the location of tanks 82 relative to connecting conduits86. In particular, engine 80 will rotate in the direction in which theupper tank 82 of an opposing pair will fall downward due to gravity whenthe connecting conduit 86 is vertically oriented. For example, theembodiment of engine 80 illustrated in FIG. 17 rotates clockwise asviewed from the perspective of FIG. 17.

Each conduit 90 is joined to the associated chamber 88 such that fluid94 is transferred from the chamber 88 to the associated tank 82 suchthat vaporization of fluid 94 occurs at a predetermined point during thecycle of operation of engine 80 which corresponds to a predeterminedposition of tanks 82. Preferably, vaporization occurs in each tank 82when the tank is in the lowermost position thereof. As will beappreciated by those of ordinary skill in the art, in order tocompensate for the finite time required for fluid 94 to traverse aconduit 90, each conduit 90 advantageously is joined to the associatedchamber 88 such that fluid 94 actually begins to flow in conduit 90slightly before the associated tank 82 reaches the aforesaidpredetermined position thereof. Further, each conduit 90 also ispreferably configured such that the end which is joined to theassociated chamber 88 is sigmoid, as shown, or otherwise bent so as toform a siphon 93 which causes fluid 94 to siphon abruptly betweenchambers 88 and the associated tanks 82. As is also shown, a furtherconduit 91 advantageously is provided which is connected between eachchamber 88 and the associated tank 82 so as to function as a vent linewhich facilitates siphoning of fluid 94 from chambers 88. Each conduit90 also is preferably joined to the associated tank 82 such thatvaporization of fluid 94 occurs within the tank at a location which thenconstitutes the uppermost region thereof. Each conduit 90 furtherpreferably communicates with the interior of the associated tank 82 viaa valve arrangement, generally denoted 95, which prevents fluid 92 fromentering conduit 90 and the associated chamber 88 when the conduit inletto another 88 is relatively lower than the conduit inlet to theassociated tank 82 and during the condensing cycle of chamber 88 whenfluid 94 is being sucked out of tank 82 by the condensation process, butwhich allows fluid 94 to contact fluid 92 for vaporization of fluid 94.

A preferred embodiment of valve arrangement 95 is illustrated which doesnot employ any moving parts, and comprises a further conduit 97 disposedwithin the associated tank 82. One end of conduit 97 communicates withthe associated conduit 90, and the other, distal, end is disclosed in alocation which constitutes the uppermost region of the interior of theassociated tank 82 when the tank is in the position during the rotationcycle therefor at which the tank becomes maximally filled with fluid 92.Preferably, the end of conduit 97 communicating with the associatedconduit 90 is enlarged, as shown, so as to maximize the surface area offluid 92 which fluid 94 initially contacts, and thereby facilitate flashvaporization of fluid 94, but without unduly restricting the volume offluid 92 which can be contained within tanks 82. Further, the interiorwall of each tank 82 is formed with a recess 99 in which the distal endof conduit 97 is disposed such that the maximum amount of fluid 94 isremoved from each tank 82 back to the associated chamber 88 as the tank82 is filled with fluid 92 and fluid 94 is condensed in the associatedchamber 88.

Tanks 82 may have any desired configuration. Chambers 88 advantageouslyare configured in a conventional manner to facilitate cooling, and hencecondensation, of volatile fluid 94, and such that the volatile fluid 94for a chamber approximately half fills the chamber when the fluid 94 isin the liquid or condensed state thereof. When the preferred embodimentof cooling arrangement 98 to be described hereinbelow is used, chambers88 advantageously also are streamlined so as to minimize hydrodynamicdrag.

A quantity of heavy fluid 92 is introduced into each pair of tanks 82which is sufficient to completely fill one of the tanks and enough tothe associated trap 87 to ensure that none of the volatile fluid 94 fora particular chamber 88 can pass from the associated tank 82 to theopposing tank 82 as heavy fluid is transferred from one tank to theother. The unfilled tank 82 of each pair of tanks, and the unfilledportion of the connecting conduit 86, and preferably evacuated tominimize the resistance to fluid transfer from one tank to the other.

Fluids which have a relatively high specific gravity are preferred forheavy fluid 92 to minimize the amount of fluid and the spacing of tanks82 from axis 84 which are required to generate a desired level oftorque. It is also desirable that fluid 92 have a low vapor pressure tominimize the possibility that fluid 92 will collect in chambers 88through condensation, and that fluid 92 be chemically compatible withvolatile fluid 94 at the operating temperatures to which fluid 92 isheated. Mercury is suitable except in applications where the high costand/or toxicity thereof preclude its use. Metals or metal alloys, suchas Wood's alloy, which have a low melting temperature, are alsopreferred when heating system 96 utilizes collector 20 describedhereinabove.

Condensation chambers 88 are partially filled with volatile fluid 94.Fluids having a low vaporization temperature and a high expansion rateare preferred for fluid 94. In an embodiment of heat engine 80 usingWood's alloy as heavy fluid 92, a formulation of Freon, such as Freon11, which is adapted to the temperature range necessary to maintain theWood's alloy in a molten state has proven satisfactory as volatile fluid94. The relative quantities of heavy fluid 92 and volatile fluid 94 tobe used are determined by the distance between opposed tanks 82, thespecific gravity of fluid 92, the expansion ratio of fluid 94, and thetemperature to which fluid 94 is heated in the gaseous phase thereof.Two grams of Freon subjected to temperatures of approximately 180° F.(82.2° C.) have proven sufficient to displace 150 pounds (68.04kilograms) of Wood's alloy between tanks 82 which are spaced 22 feet(6.7 meters) apart.

Any conventional heating and cooling arrangements advantageouslyconstitute heating and cooling systems 96 and 98, respectively. Heatingsystem 96 advantageously is adapted to maintain heavy fluid 92 at arelatively constant elevated temperature, and cooling system 98advantageously is adapted to intermittently cool each condensationchamber 88 during a predetermined portion of the operating cycle of heatengine 80, as will be described in more detail hereinbelow.

Combined apparatus constituting systems 96 and 98 is illustrated in FIG.18, and comprises a housing 100 in which tanks 82, chambers 88, andconduits 86 and 90 are disposed. Advantageously, tanks 82 and chambers88 are fixedly mounted to housing 100 and housing 100 is mounted forrotation abous axis 84. As shown, tanks 82 are spaced from chambers 88longitudinally with respect to axis 84, and housing 100 is configured todefine a first jacket 102 enclosing tanks 82 and conduits 86, and asecond jacket 104, preferably spaced from jacket 102 and thermallyisolated therefrom by insulation 106, enclosing chambers 88. A heatingfluid 108 is supplied to jacket 102 from a source 110 and a coolingfluid 112 is supplied to jacket 104 from a source 114 through axialopenings 116 and 118, respectively, formed in opposite sides of housing100. Preferably, jacket 102 is maintained completely filled with heatingfluid 108, such that tanks 82 are completely immersed in a bath ofheating fluid, while jacket 104 is maintained only partially filled,such that chambers 88 pass into and out of a bath of cooling fluid 112as they rotate about axis 84. The level of cooling fluid 112 in jacket104 is preferably below the axis of rotation 84, such that each tank 82has passed the midpoint of its downward displacement before theassociated chamber 88 enters fluid 112. As will be appreciated by thoseof ordinary skill in the art, the relative level of fluid 112 isdetermined in dependence on the temperature differential between heavyfluid 92 and cooling fluid 112, the rotational speed of engine 80, andthe transfer time required for passage of a given volume of fluid 92between associated tanks 82.

Advantageously, heated water or oil, or the like, constitutes heatingfluid 108, and collector 20 described hereinabove constitutes source110. Any conventional refrigerant, including relatively cool water,advantageously constitutes cooling fluid 112. The greater is thedifference in temperature between heating fluid 108 and cooling fluid112, the faster tends to be the speed of rotation of tanks 82 about axis84.

The operation of heat engine 80 will now be described with reference tothe four tank embodiment shown in FIG. 17. For convenience, tanks 82have been lettered A, B, C, and D, and the corresponding expansionchambers 88 have been designated a, b, c, and d.

As noted hereinabove, tanks 82 rotate clockwise about axis 84 whenviewed from the perspective of FIG. 17. Tanks 82 become filled withheavy fluid 92 as they rotate through the half cycle wherein they aredescending with respect to the vertical, and are emptied as they rotatethrough the half cycle wherein they are ascending with respect to thevertical. Opposing tanks 82 are filled and emptied 180° out of phasewith each other as the heavy fluid 92 contained therein is transferredback and forth between the tanks. Transfer of fluid 92 commences when afilled tank 82, for example, tank A in FIG. 17, reaches the lowermostposition thereof and volatile fluid 94 in a condensed state travels fromthe associated condensation chamber "a" through conduit 90 and contactsfluid 92. Since fluid 92 is heated, fluid 94 effectively "flash"vaporizes, and the resulting gaseous expansion acts directly on fluid 92to force it upwardly from tank A through the connecting conduit 86 toemptied tank B. The weight of heavy fluid 92 in tank B provides thimpetus or momentum for displacement of tank B from the uppermostposition thereof downwardly through the cycle of rotation toward thevertically lowermost position thereof. Maximum efficiency is obtainedfrom the expansion energy of fluid 94 because as tank A empties and tankB fills, a constantly decreasing quantity of fluid 92 need be displaceda constantly decreasing vertical distance.

Preferably, transfer of fluid 92 from tank A to tank B is substantiallycompleted by the time tanks A and B have reached the midpoints of theirrespective vertical displacements. At this stage, the condensing cyclefor the vaporized fluid 94 from condensation chamber "a" commences. Withthe preferred embodiment of cooling system 98 illustrated in FIG. 18 anddescribed hereinabove, synchronization of the condensing cycle isachieved automatically because, as tank B passes the midpoint of itsdownward displacement, chamber "a" enters cooling fluid 112 and iscooled thereby, thus inducing condensation of fluid 94 in chamber "a".In addition, as chamber "a" becomes relatively lower vertically thantank A, additional fluid is induced by gravity to travel toward chamber"a", where it is condensed. Condensation of fluid 94 in chamber "a"continues as chamber "a" continues its arc of travel through coolingfluid 112, and the now emptied tank A travels upwardly to the verticallyhighest position thereof.

When tank A reaches the vertically highest position thereof, transfer offluid 92 thereto from the now filled tank B commences in the same manneras that described above when tank B was in the vertically highestposition thereof. Condensation of fluid 94 preferably ceases as tank Arotates downwardly to the midpoint of its vertical displacement. This isachieved automatically with the embodiment of cooling system 98 shown inFIG. 18 and described hereinabove because by the time tank A reaches themidpoint of its downward displacement, chamber "a" has emerged fromcooling fluid 112. As will be appreciated by those of ordinary skill inthe art, cessation of the cooling of chamber "a" for a period of timeprior to the vaporization of fluid 94 minimizes the degree to whichfluid 94 prematurely condenses in chamber "a" during the vaporizationphase, and thus maximizes the expansion energy which is available fordisplacement of fluid 92. The identical cycle is followed in the case oftanks C and D.

As will be appreciated by those of ordinary skill in the art, the rateof exchange, or cycle time for fluid 94 to expand and condensedetermines the speed of rotation of tanks 82 about axis 84. The specificgravity of fluid 92 and the distance it travels during the displacementof a tank 82 from the uppermost position thereof to the lowermostposition thereof determines the foot-pounds of torque production, whichcan be readily converted into various other forms of mechanical orelectrical energy, as is well known in the art.

Although the invention has been described with respect to exemplaryembodiments thereof, it will be understood that variations andmodifications can be effected in the embodiments without departing fromthe scope or spirit of the invention.

I claim:
 1. A solar heat collector comprising solar absorber means forconverting solar radiation into heat,a heat transfer liquid fortransferring heat from said solar absorber means, means defining atleast one passage for providing flow of said heat transfer liquid incontact with said solar absorber means and for enabling solar radiationto pass through the heat transfer liquid during the flow thereof throughsaid at least one passage, means, including a pump, for pumping saidheat transfer fluid through said at least one passage to provide heatingthereof by solar radiation and for supplying the heat transfer liquidfor utilization after heating thereof in said at least one passage; andmeans for creating a relative vacuum in said at least one passage so asto minimize the creation of a stagnant boundary layer of said heattransfer liquid in contact with said solar absorber means when said heattransfer liquid is pumped through said at least one passage.
 2. Thesolar heat collector of claim 1 wherein said heat transfer liquid issubstantially transparent to solar IR radiation and has a lowreradiation factor for long wave IR heat.
 3. The solar heat collector ofclaim 2 wherein said heat transfer liquid is selected from the group ofmineral oil, aliphatic hydrocarbon oils, and silicone oils.
 4. The solarheat collector of claim 1 wherein said solar absorber means defines agrooved surface facing the sun and forming a plurality of grooves andridges, said passage defining means comprises a flexible membrane whichis substantially transparent to solar IR radiation disposed in overlyingrelationship with said solar absorber grooved surface for sealingcontact with said grooved surface ridges when said grooved surfacegrooves are subjected to a vacuum.
 5. The solar heat collector of claim1 wherein said solar absorber means defines a grooved surface facing thesun and forming a plurality of alternating triangularshaped teeth andgrooves having a vertex angle of at least approximately 60°.
 6. Thesolar heat collector of claim 5 wherein said grooves have a depth ofless than approximately one-quarter centimeter.
 7. A solar heatcollector comprising heat radiation, said solar absorbing means defininga surface for receiving solar radiation,a heat transfer fluid fortransferring heat from said solar absorber means selected from the groupof mineral oil, aliphatic hydrocarbon oils, and silicone oils, passagemeans, defining at least one passage, for passing said heat transferliquid in surface contact over at least a portion of said solarabsorbing means surface in a film having a thickness such that said filmof heat transfer fluid is substantially transparent to shortwave IRsolar radiation and has a low reradiation factor for longwave IR heat;and vacuum means for creating a relative vacuum in said at least onpassage so as to minimize the creation of a stagnant boundary layer incontact with the surface defined by said solar radiation means when saidheat transfer fluid is passed through said at least one passage.
 8. Asolar heat collector comprisingsolar absorber means for converting solarradiation into heat, said solar absorber means having a grooved surfaceincluding at least one groove therein, a sheet for covering said atleast one groove, said sheet being substantially transparent to at leastsolar IR radiation vacuum means for maintaining said sheet in sealingengagement with said grooved surface through the action of a vacuum suchthat said sheet and said at least one groove form a correspondingpassage through which a heat transfer liquid flows; and means forsupplying said heat transfer liquid, after heating by solar radiation insaid passage, to a thermal load.
 9. The solar heat collector of claim 8wherein said grooved surface is a solar radiation receiving surface. 10.The solar heat collector of claim 8 or 9 wherein said vacuum meanscomprisesmeans for supporting said sheet in overlying relationship withsaid absorper surface, and means for creating a relative vacuum betweensaid absorber surface and said sheet.
 11. The solar heat collector ofclaim 10 wherein said sheet is relatively flexible so as to facilitateformation of said at least one passage.
 12. The solar heat collector ofclaim 11 wherein said sheet has sufficient rigidity that deformation ofa corresponding at least one portion of said sheet forming said at leastone passage is minimized.
 13. The solar heat collector of claim 11wherein said sheet is supported under tension such that deformation of acorresponding at least one portion of said sheet forming said at leastone passage is minimized.
 14. The solar heat collector of claim 10wherein a sufficient vacuum is created to allow heat transfer liquid tobe pumped through said at least one passage at an accelerated rate suchthat a liquid pressure is created which causes improved surface contactbetween the heat transfer fluid and said grooved surface.
 15. The solarheat collector of claim 10 wherein said grooved surface defines aplurality of alternating grooves and ridges and a trough at each endthereof for distributing heat transfer liquid to and collecting heattransfer liquid from said grooves, and said sheet sealingly engages saidridges such that said grooves and said sheet form a plurality of saidpassages which are discrete from one another.
 16. The solar heatcollector of claim 15 wherein said collector further comprises meanscovering each of said troughs for supporting said sheet such that theinterfaces between said troughs and said passages are substantiallyuniform in size and thereby secure uniformity of flow through all ofsaid passages.
 17. The solar heat collector of claim 9 wherein saidsheet is substantially reflective and nonabsorptive to longwave heat.18. The solar heat collector of claim 17 wherein said sheet issufficiently elastic to accommodate dimensional changes in said solarabsorbing means caused by changes in the temperature thereof.
 19. Thesolar heat collector of claim 18 wherein said sheet is formed from a"Tedlar" membrane.
 20. The solar heat collector of claim 19 wherein saidsheet is 0.05 millimeters thick.